38 P7M{c Parks. 



these, vegetable forms they could not live.* They keep the water 

 pure, and yield oxygen to the atmosphere. In every pool and stag- 

 nant ditch, under the influence of heat, algae are quickly produced, 

 forming the green scum over them, w^hich instead of being injurious, 

 are beneficial, and emit oxygen in the shape of beads that can be 

 seen on any sunny day. It is only after the pool is dried, and 

 these conferviE are wafted away by the wind, that places of this 

 character become injurious. The amount of benefit derived from 

 these apparently insignificant plants, is great when we take into 

 account the many extensive surfaces of water dispersed over the 

 world, which are thus kept pure, and made subservient to a healthy 

 state of the atmosphere. It is not only vast, but part of the harmo- 

 nious whole, and worthy of Him who has appointed even to the 

 meanest of His creatures, something to do for the good of His 

 creation ;f and well may it be said — 



" Call us not weeds, we are the flowers of the sea." 

 INFLUENCE OF VEGETATION, PARTICULARLY TREES, UPON HEALTH. 



Having thus shown the actions and reactions which take place 

 between animal and vegetable life, and how dependent the former is 

 upon the latter, we propose to call attention to a series of facts, 

 gathered from different sources, which illustrate in a marked degree, 

 the application of these principles, clearly proving that the infection 

 and diffusion of malaria or noxious emanations are arrested by trees, 

 whose structure and canopy of foliage act in a three-fold capacity ; 

 — first as a barrier to break the flow, second as an absorbent of those 

 emanations, and third as eliminators of oxygen. 



Lancisi cites a number of facts showing the protection afforded 

 by belts of trees against the effects of malaria, and the danger 

 resulting from their removal. He calls attention to the fact that, in 

 former days, there existed on the south side of Rome a thick forest 

 which extended from Frascati and Albano to the Tiber, and pi'otected 

 the southern portion of the city and the neighboring district from 

 the baneful influence of the effluvia of the Pontine Marshes. This 



* " The parlor aquarium has taught even those to whom it is but an amusing toy, that the balance 

 of animal and vegetable life must be preserved, and that excess of either is fatal to the other, in the 

 artificial tank as well as in natural water. A few years ago, the water of the Cochituate Aqueduct, at 

 Boston, became so offensive in smell and taste, as to be quite unfit for use. Scientific investigation found 

 the cause in the scrupulous care with which aquatic vegetation had been excluded from the reservoir, 

 and the consequent death and decay of the animalculae which could not be shut out nor live in the water 

 without the the vegetable element." — Man and Nature: Marsh. 



'^Contributions to the History of Marine AJgce of North America: Harvey- 



